Helical concave



FIG. 1 is a front right perspective view of the helical concave showing our new design;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a right side view thereof;

FIG. 6 is a top right perspective view thereof; and,

FIG. 7 is a top left perspective view thereof. 

The ornamental design for a helical concave, as shown and described. 